J Korean Orthop Assoc.  2011 Aug;46(4):320-325. 10.4055/jkoa.2011.46.4.320.

Accuracy of Inter Femoral Head Center Distance Measurement and Evaluation for Coronal Alignment of Femoral Component during Total Knee Arthroplasty

• Jung WH
• Kim DH
• Chun CW
• Jeong JH
• Ha YC
• Seo JG

• KMID: 2185430
• DOI: http://doi.org/10.4055/jkoa.2011.46.4.320

Abstract

PURPOSE
Alignment is an important factor in the long-term success of total knee arthroplasty. In the total knee arthroplasty, the conventional extramedullary femoral alignment system has significant error in femoral coronal alignment, since it is difficult to find the femoral head center and it is time consuming to determine during the operation. The purpose of our study was to evaluate the accuracy of the newly-designed marker system for extramedullary femoral alignment that uses radiologic distance between the 2 femoral head centers.
MATERIALS AND METHODS
Between July 2008 and July 2009, 90 patients (100 knees) with knee osteoarthritis underwent total knee arthroplasty using the femoral extramedullary femoral guide system. We measured the distance between the femoral head centers using the radiologic picture archiving and communication system (PACS, General Electric, Milwaukee, WI) system preoperatively, then plastic rods and metal pegs were used to simulate the inter femoral head center distance. By placing the center of the plastic rod after marking the inter femoral head center distance on the central body line, we could trace the coronal mechanical axis. We measured the angle between the femoral mechanical axis and the femoral component in standing long leg antero-posterior radiograph to assess radiologically the accuracy of coronal alignment postoperatively.
RESULTS
The average femoral length in the study group was 402.5+/-16.2 mm. The mean distance between the femoral head and the center of the marker was 49.6+/-17.9 mm. The average error in estimation of the distance between the femoral head center and the metal peg of the marker was 3.78+/-3.14 mm. The positional error in alignment was 1degrees or less in 90% and 2degrees or less in 100% of knees. The average angle of femoral component to femoral mechanical axis was 89.9+/-1.5degrees (range 84.4-93.6degrees). The coronal alignment of the femoral components was within 90degrees+/-3degrees in -96% of cases.
CONCLUSION
Our results suggest that the clinical method reported here is a simple and reliable method to localize the center of the femoral head during total knee arthroplasty.

Keyword

total knee arthroplasty; mechanical axis; extramedullary femoral guide system; interfemoral head center distance

MeSH Terms

Arthroplasty
Axis, Cervical Vertebra
Head
Humans
Knee
Leg
Osteoarthritis, Knee
Plastics
Radiology Information Systems
Plastics

Figure

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  Figure 1 (A) 100mm X-Ray Magnification Maker (B) X-ray shows calculation of the interfemoral head center distance. (C) The Mechanical Axis Marker is placed on the body center.

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  Figure 2 The Mechanical Axis Marker: the plastic rod and metal pegs were used to simulate the inter femoral head center distance.

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  Figure 3 A radiograph was taken after positioning of the patient before surgery. We measured horizontal distance from the peg to the perpendicular extending line through the line of the femoral head center.

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  Figure 4 Radiograph showing the mechanical axis in the coronal plane. The alignment of the coronal femoral components was measured by the intersection of a line drawn across the base of each component and the mechanical axis. FFA, frontal femoral angle.

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  Figure 5 Drawing shows the acceptable range of error in Mechanical Axis Marker placement.

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